A shared line appearance feature allows a number of stations to share a common directory number on a line appearance of each of the telephone station sets. If a caller places a call to the directory telephone number, any one of the telephone station sets having a line appearance for that telephone number can answer the telephone call. After one of the telephone station sets has answered the call, another telephone station set can be added to the telephone call simply by the other station set picking up on the line appearance. Similar operations are performed with respect to one of the telephone station sets placing an outgoing call. The state of the line appearance is displayed on all telephone station sets terminating that telephone directory number. The shared line appearance feature has proven particularly useful in the business environment.
Whereas prior art telecommunication switching systems have offered the shared line appearance feature, a problem in the prior art has been that all of the telephone stations sets involved in the shared line appearance had to be directly connected to one telecommunication system. This restriction has proven to be a problem with respect to private networks of business telecommunication systems (also referred to as PBXs) and the Centrex service.